1. Field of the Invention
The present invention relates generally to magneto-optical recording media and particularly to those providing a heat sink effect.
2. Description of the Background Art
Magneto-optical recording media have been noted as a recording medium which is rewritable, has a large recording capacity and is highly reliable, and they are put to use for example as computer memory. Furthermore recently a magneto-optical recording medium provided in the form of a 120 mmxcfx86 disc having a storage capacity of 6 Gbytes is about to be put to use as an Advanced Storage Magneto-Optical (AS-MO) disk standard. To reproduce a signal from such a high-density magneto-optical recording medium a laser beam is directed thereto to form at a reproducing layer thereof a detection window smaller than the laser beam""s spot diameter and a magnetic domain of the recording layer is transferred to the detection window and the transferred magnetic domain is thus detected. This technique is referred to as magnetically induced super resolution (MSR).
Furthermore, there has also been developed a technique applying an alternate magnetic field to a magneto-optical recording medium and transferring a magnetic domain from a recording layer to a reproducing layer and enlarging the transferred magnetic domain to reproduce a signal. Using this magnetic-domain enlargement and reproduction technique, there has also been suggested a magneto-optical recording medium having a recording capacity of 14 Gbytes.
A magneto-optical recording medium is irradiated with a laser beam to record or reproduce a signal. As such, to diffuse heat generated through the laser beam radiation, to prevent the laser beam""s focus from blurring, and to prevent a magnetic layer of the recording medium from being oxidized, the recording medium has sputtered on a substrate a magnetic layer including a recording layer and a reproducing layer, and a protection layer, e.g., of SiN and/or a heat diffusing layer for example of Al then added thereon.
More specifically, with reference to FIG. 14, a conventional magneto-optical recording medium 70 has a transparent substrate 71 and has formed thereon an underlying layer 72 formed of SiN, a reproducing layer 73 formed of GdFeCo, a non-magnetic layer 74 formed of SiN, a recording layer 75 formed of TbFeCo, a protection layer 76 formed of SiN and a heat diffusing layer 77 formed of Al, successively stacked in layers, as seen in cross section. In general, after heat diffusing layer 77 is formed UV ray cured resin or the like is used to coat the recording medium to prevent the recording medium from being oxidized and damaged.
Heat diffusing layer 77, provided after reproducing layer 73 and recording layer 75 are sputtered, also prevents reproducing layer 73 and recording layer 75 from being oxidized. As such, heat diffusing layer 77 is provided opposite to transparent substrate 71.
However, as its recording density increases, recording layer 75 has formed therein a magnetic domain reduced in size. As such, when in reproducing a signal a laser beam is directed to the recording medium and a detection window is formed in reproducing layer 73, a plurality of magnetic domains are transferred from recording layer 75 to the detection window formed in reproducing layer 73. Thus, accurate signal reproduction cannot be achieved.
More specifically, conventional magneto-optical recording medium 70 has reproducing layer 73 posed between SiN forming underlying layer 72 and SiN forming non-magnetic layer 74. As such, the heat generated in reproducing layer 73 through laser beam radiation is not so much emitted therefrom. This increases a region heated to a temperature allowing a magnetic domain of recording layer 75 to be transferred. Consequently, a plurality of magnetic domains are transferred from recording layer 75 to reproducing layer 73 and accurate signal reproduction can thus not be achieved.
The present invention therefore contemplates a magneto-optical recording medium capable of forming in a reproducing layer a detection window having a size approximately corresponding to a shortest length of a magnetic domain formed in a recording layer.
The present invention provides a magneto-optical recording medium including a recording layer having formed therein a magnetic domain magnetized according to a signal to be recorded, a reproducing layer receiving the magnetic domain transferred from the recording layer, and a heat sink layer formed in contact with the reproducing layer and the recording layer and blocking exchanging-coupling between the reproducing layer and the recording layer.
When the present magneto-optical recording medium is irradiated with a laser beam, the reproducing layer generates heat, which diffuses from the reproducing layer to the heat sink layer and the reproducing layer has in an in-plane direction thereof a steep temperature profile. The reproducing layer has formed therein a detection window each receiving an individual magnetic domain transferred from the recording layer. Furthermore, the heat sink layer is provided also in contact with the recording layer. As such, the heat generated in the recording layer through laser beam radiation also diffuses from the recording layer to the heat sink. layer to allow the recording layer to have a steep temperature profile. Thus in the present invention if the recording layer has a magnetic domain reduced in length each magnetic domain of the recording layer can be detected with high resolution. Furthermore in the present invention the recording layer can have formed therein a magnetic domain reduced in length to record a signal densely.
Furthermore the present invention provides a magneto-optical recording medium including a recording layer having formed therein a magnetic domain magnetized according to a signal to be recorded, a first reproducing layer receiving the magnetic domain transferred from the recording layer, a second reproducing layer receiving the magnetic domain transferred to the first reproducing layer and further transferred from the first reproducing layer through magnetostatic-coupling, and a heat sink layer formed in contact with the first reproducing layer and the recording layer and blocking exchanging-coupling between the first reproducing layer and the recording layer, wherein the second reproducing layer is formed of a magnetic material allowing the transferred magnetic domain to be enlarged by an external magnetic field.
When the present magneto-optical recording medium is irradiated with a laser beam, the first reproducing layer generates heat, which diffuses from the first reproducing layer to the heat sink layer to allow the first reproducing layer to have in an in-plane direction thereof a steep temperature profile. The recording layer has formed therein a detection window each receiving an individual magnetic domain transferred from the recording layer through magnetostatic-coupling. The magnetic domain transferred to the first reproducing layer is further transferred to the second reproducing layer through magnetostatic-coupling. The magnetic domain transferred to the second reproducing layer is enlarged by an external magnetic field and detected by a laser beam directed thereto. Furthermore, the heat sink layer is provided also in contact with the recording layer. As such, the heat generated in the recording layer through laser beam radiation also diffuses from the recording layer to the heat sink layer to allow the recording layer to have a steep temperature profile. Thus in the present invention if the recording layer has a magnetic domain reduced in length each magnetic domain of the recording layer can be detected in the first reproducing layer with high resolution and also enlarged and thus reproduced in the second reproducing layer. Furthermore in the present invention the recording layer can have formed therein a magnetic domain reduced in length to allow a signal to be recorded densely.
Furthermore the present invention provides a magneto-optical recording medium including a recording layer having formed therein a magnetic domain magnetized according to a signal to be recorded, a first heat sink layer formed in contact with the recording layer, a reproducing layer receiving a magnetic domain transferred from the recording layer through magnetostatic-coupling, and a second heat sink layer formed in contact with the reproducing layer.
When the present magneto-optical recording medium is irradiated with a laser beam, the recording layer stores heat, which is absorbed by the first heat sink layer, and the reproducing layer stores heat, which is absorbed by the second heat sink layer. Thus the reproducing layer and the recording layer each have in an in-plane direction thereof a steep heat distribution. Thus in the present invention a short magnetic domain can be used to record a signal in the recording layer densely. Furthermore, the short magnetic domain formed in the recording layer can be detected in the reproducing layer with high resolution.
Furthermore, the present invention provides a magneto-optical recording medium including a recording layer having formed therein a magnetic domain magnetized according to a signal to be recorded, a first heat sink layer formed in contact with the recording layer, a first reproducing layer receiving a magnetic domain transferred from the recording layer through magnetostatic-coupling, a second heat sink layer formed in contact with the first reproducing layer, and a second reproducing layer receiving the magnetic domain transferred to the first reproducing layer and further transferred from the first reproducing layer through magnetostatic-coupling, wherein the second reproducing layer is formed of a magnetic material allowing the transferred magnetic domain to be enlarged by an external magnetic field.
When the present magneto-optical recording medium is irradiated with a laser beam, the recording layer stores heat, which is absorbed by the first heat sink layer, and the first reproducing layer stores heat, which is absorbed by the second heat sink layer. Thus, the first reproducing layer and the recording layer each have in an in-plane direction thereof a steep temperature profile. Thus, a magnetic domain is transferred from the recording layer to the first reproducing layer through magnetostatic-coupling with high resolution and the magnetic domain is further transferred from the first reproducing layer to the second reproducing layer through magnetostatic-coupling. The magnetic domain transferred to the second reproducing layer is enlarged by an external magnetic field and detected by a laser beam. Thus in the present invention a short magnetic domain can be formed in the recording layer to allow a signal to be recorded densely. Furthermore, the short magnetic domain formed in the recording layer can be transferred to the first reproducing layer with high resolution and the magnetic domain thus transferred can be enlarged and thus reproduced in the second reproducing layer.
Furthermore the present invention provides a magneto-optical recording medium including a recording layer having formed therein a magnetic domain magnetized according to a signal to be recorded, a non-magnetic layer formed in contact with the recording layer, a reproducing layer formed in contact with the non-magnetic layer and receiving the magnetic domain transferred from the recording layer, and a heat sink layer formed in contact with the reproducing layer.
When the present magneto-optical recording medium is irradiated with a laser beam, the reproducing layer stores heat, which is absorbed by the heat sink layer formed of a magnetic material. Thus the reproducing layer has in an in-plane direction thereof a steep temperature profile. Thus a magnetic domain is transferred from the recording layer via the non-magnetic layer to the reproducing layer through magnetostatic-coupling with high resolution. As such in the present invention the heat sink layer provided on a side receiving a laser beam can absorb the heat stored in the reproducing layer, to transfer a magnetic domain to be transferred to the reproducing layer with high resolution.
Preferably, the magneto-optical recording medium including the heat sink layer provided in contact with the reproducing layer and the recording layer satisfies (Pcxc3x97Tex)/(pxc3x97t)xe2x89xa61, wherein Tex represents a minimal film thickness required to block exchanging-coupling, Pc represents a heat conductivity of a material of the reproducing layer higher than a heat conductivity of any other material of the reproducing layer at room temperature, p represents a heat conductivity of a material of the heat sink layer at room temperature and t represents a thickness of the heat sink layer, t being larger than Tex.
In the present magneto-optical recording medium, the heat sink layer diffuses more heat than the reproducing layer. More specifically, when the magneto-optical recording medium is irradiated with a laser beam, the reproducing layer stores heat, which is absorbed by the heat sink layer. Furthermore, the heat sink layer locks the exchanging-coupling between the recording layer and the reproducing layer. Thus the present invention can transfer a magnetic domain from the recording layer to the reproducing layer through magnetostatic-coupling and also reduce in size a region of a reproducing layer receiving the magnetic domain transferred thereto.
Preferably, the magneto-optical recording medium including the heat sink layer provided in contact with the first reproducing layer and the recording layer and the second reproducing layer formed of a magnetic material having a magnetic domain enlarged by an external magnetic field, satisfies (Pcxc3x97Tex)/(pxc3x97t)xe2x89xa61, wherein Tex represents a minimal film thickness required to block exchanging-coupling, Pc represents a heat conductivity of a material of the first reproducing layer higher than a heat conductivity of any other material of the first reproducing layer at room temperature, p represents a heat conductivity of a material of the heat sink layer at room temperature and t represents a thickness of the heat sink layer, t being larger than Tex.
In the present magneto-optical recording medium the heat sink layer diffuses more heat than the first reproducing layer. More specifically, when the magneto-optical recording medium is irradiated with a laser beam, the first reproducing layer stores heat, which is absorbed by the heat sink layer. Furthermore, the heat sink layer blocks the exchanging-coupling between the recording layer and the first reproducing layer. The first reproducing layer receives a magnetic domain transferred thereto, which is in turn transferred to the second reproducing layer through magnetostatic-coupling and also enlarged. Thus the present invention can reduce in size a region of the first reproducing layer receiving a magnetic domain transferred thereto and transfer a magnetic domain from the recording layer to the first reproducing layer with high resolution and also enlarge the transferred magnetic domain and detect the enlarged magnetic domain.
Preferably, the magneto-optical recording medium including the heat sink layer provided for the recording layer and the heat sink layer provided for the reproducing layer satisfies (Pcxc3x97Tex)/(pxc3x97t)xe2x89xa61, wherein Tex represents a minimal film thickness required to block exchanging-coupling, Pc represents a heat conductivity of a material of the reproducing layer higher than a heat conductivity of any other material of the reproducing layer at room temperature, p represents a heat conductivity of a material of the second heat sink layer at room temperature and t represents a thickness of the second heat sink layer, t being larger than Tex.
In the present magneto-optical recording medium the second heat sink layer diffuses more heat than the reproducing layer. More specifically, when the magneto-optical recording medium is irradiated with a laser beam, the reproducing layer stores heat, which is absorbed by the second heat sink layer. Furthermore, the recording layer has a magnetic domain transferred to the reproducing layer through magnetostatic-coupling. Thus the present invention ensures that the heat stored in the reproducing layer is absorbed by the second heat sink layer. This can reduce in size a region of the reproducing layer receiving a magnetic domain transferred thereto.
Preferably, the magneto-optical recording medium including the heat sink layer provided for the recording layer, the heat sink layer provided for the reproducing layer, the first reproducing layer receiving a magnetic domain transferred from the recording layer, and the second reproducing layer receiving a magnetic domain transferred from the first reproducing layer, satisfies (Pcxc3x97Tex)/(pxc3x97t)xe2x89xa61, wherein Tex represents a minimal film thickness required to block exchanging-coupling, Pc represents a heat conductivity of a material of the first reproducing layer higher than a heat conductivity of any other material of the first reproducing layer at room temperature, p represents a heat conductivity of a material of the second heat sink layer at room temperature and t represents a thickness of the second heat sink layer, t being larger than Tex.
In the present magneto-optical recording medium the second heat sink layer diffuses more heat than the first reproducing layer. More specifically, when magneto-optical recording medium is irradiated with a laser beam, the first reproducing layer stores heat, which is absorbed by the second heat sink layer. Furthermore, the recording layer has a magnetic domain transferred to the first reproducing layer through magnetostatic-coupling and in turn further transferred to the second reproducing layer through magnetostatic-coupling. In the second reproducing layer the transferred magnetic domain is enlarged and also detected. Thus the present invention can reduce in size a region of the first reproducing layer receiving a magnetic domain transferred thereto and transfer a magnetic domain from the recording layer to the first reproducing layer with high resolution and also enlarge the transferred magnetic domain and reproduce the enlarged magnetic domain.
Preferably, the magneto-optical recording medium including the heat sink layer provided in contact with the reproducing layer and opposite to the recording layer, satisfies (Pcxc3x97Tex)/(pxc3x97t)xe2x89xa61, wherein Tex represents a minimal film thickness required to block exchanging-coupling, Pc represents a heat conductivity of a material of the reproducing layer higher than a heat conductivity of any other material of the reproducing layer at room temperature, p represents a heat conductivity of a material of the heat sink layer at room temperature and t represents a thickness of the heat sink layer, t being larger than Tex.
In the present magneto-optical recording medium the heat sink layer diffuses more heat than the reproducing layer. More specifically, when the magneto-optical recording medium is irradiated with a laser beam, the reproducing layer stores heat, which is absorbed by the heat sink layer. Furthermore, the recording layer has a magnetic domain transferred to the reproducing layer and the heat sink layer through magnetostatic-coupling. Thus the present invention ensures the heat stored in the reproducing layer is absorbed by the heat sink layer. Consequently the present invention can reduce in size a region of the reproducing layer receiving a magnetic domain transferred thereto and transfer a magnetic domain from the recording layer to the reproducing layer with high resolution and also detect the transferred magnetic domain with high signal intensity.
Preferably, the magneto-optical recording medium can have the heat sink layer provided in contact with the reproducing layer and the recording layer that is formed of a non-magnetic material.
When the present magneto-optical recording medium is irradiated with a laser beam, the reproducing layer stores heat, which is absorbed by the heat sink layer. Furthermore, the recording layer has a magnetic domain transferred to the reproducing layer via the heat sink layer through magnetostatic-coupling. As such in the present invention inserting a non-magnetic material between the reproducing layer and the recording layer allows the reproducing layer to emit heat and the recording layer and the reproducing layer to transfer a magnetic domain from the former layer to the latter layer through magnetostatic-coupling.
Preferably, the magneto-optical recording medium including the heat sink layer provided in contact with the first reproducing layer and the recording layer and the second reproducing layer formed of a magnetic material having a magnetic domain enlarged with an external magnetic field, can have the heat sink layer formed of a non-magnetic material.
When the present magneto-optical recording medium is irradiated with a laser beam, the first reproducing layer stores heat, which is absorbed by the heat sink layer. Furthermore, the recording layer has a magnetic domain transferred to the first reproducing layer via the heat sink layer through magnetostatic-coupling and in turn enlarged by an external magnetic field. As such in the present magneto-optical recording medium enlarging a magnetic domain to reproduce a signal a non-magnetic material can be inserted between the recording layer and the reproducing layer to allow the reproducing layer to emit heat and the recording layer and the reproducing layer to transfer a magnetic domain from the former layer to latter layer through magnetostatic-coupling.
Preferably, the magneto-optical recording medium including the first heat sink layer provided for the recording layer and the second heat sink layer provided for the reproducing layer, can have the second heat sink layer formed of a non-magnetic material.
When the present magneto-optical recording medium is irradiated with a laser beam, the recording layer stores heat, which is absorbed by the first heat sink layer, and the reproducing layer stores heat, which is absorbed by the second heat sink layer formed of a non-magnetic material. Furthermore, the recording layer has a magnetic domain transferred to the reproducing layer through magnetostatic-coupling. As such, using a non-magnetic material to form the heat sink layer provided for the reproducing layer, allows the heat of the reproducing layer to be absorbed and the recording layer and the reproducing layer to transfer a magnetic domain from the former layer to the latter layer through magnetostatic-coupling.
Preferably, the magneto-optical recording medium including the heat sink layer provided for the recording layer, the heating emitting layer provided for the reproducing layer, the first reproducing layer receiving a magnetic domain transferred from the recording layer, and the second reproducing layer receiving a magnetic domain transferred from the first reproducing layer, can have the second heat sink layer formed of a non-magnetic material.
When the present magneto-optical recording medium is irradiated with a laser beam, the recording layer stores heat, which is absorbed by the first heat sink layer, and the first reproducing layer stores heat, which is absorbed by the second heat sink layer formed of a non-magnetic material. Furthermore, the recording layer has a magnetic domain transferred to the first reproducing layer through magnetostatic-coupling and in turn further transferred to the second reproducing layer through magnetostatic-coupling. The magnetic domain transferred to the second reproducing layer is enlarged by an external magnetic field and thus detected. As such the magneto-optical recording medium enlarging a magnetic domain to reproduce a signal including the first heat sink layer provided for the first reproducing layer that is formed of a non-magnetic material, allows the heat of the first reproducing layer to be absorbed and the recording layer and the first reproducing layer to transfer a magnetic domain from the former layer to the latter layer through magnetostatic-coupling.
Preferably, the magneto-optical recording medium including the heat sink layer provided in contact with the reproducing layer and opposite to the recording layer, can have the heat sink layer formed of a non-magnetic material.
When the present magneto-optical recording medium is irradiated with a laser beam, the reproducing layer stores heat, which is absorbed by the heat sink layer formed of a non-magnetic material. As such, using a non-magnetic material to form the heat sink layer and providing it on the side receiving the laser beam allows a magnetic domain to be transferred from the recording layer to the reproducing layer with high resolution.
Preferably, the magneto-optical recording medium including the heat sink layer provided in contact with the reproducing layer and the recording layer, can have the heat sink layer formed of a magnetic material having a Curie temperature lower than a temperature allowing a signal to be reproduced.
When the present magneto-optical recording medium is irradiated with a laser beam, the reproducing layer stores heat, which is absorbed by the heat sink layer. When a temperature allowing a signal to be reproduced is reached, the heat sink layer is no longer magnetized. Thus in the present invention providing the heat sink layer formed of a magnetic material having a low Curie temperature allows the reproducing layer to emit heat and the recording layer and the reproducing layer to transfer a magnetic domain from the former layer to the latter layer through magnetostatic-coupling.
Preferably, the magneto-optical recording medium including the heating emitting layer provided in contact with the first reproducing layer and the recording layer and the second reproducing layer formed of a magnetic material allowing a magnetic domain to be enlarged by an external magnetic field, can have the heat sink layer formed of a magnetic material having a Curie temperature lower than a temperature allowing a signal to be reproduced.
When the present magneto-optical recording medium is irradiated with a laser beam, the first reproducing layer stores heat, which is absorbed by the heat sink layer. When a temperature allowing a signal to be reproduced is reached, in the heat sink layer is no longer magnetized, and a magnetic domain is transferred from the recording layer to the first reproducing layer through magnetostatic-coupling. Furthermore the magnetic domain is further transferred from the first reproducing layer to the second reproducing layer through magnetostatic-coupling. Thus in the present invention providing the magneto-optical recording medium enlarging a magnetic domain to reproduce a signal with the heat sink layer formed of a magnetic material having a low Curie temperature allows the first reproducing layer to emit heat and the recording layer and the first reproducing layer to transfer a magnetic domain from the former layer to the latter layer through magnetostatic-coupling.
Preferably, the magneto-optical recording medium including the heat sink layer provided for the recording layer and the heat sink layer provided for the reproducing layer can have the second heat sink layer formed of a magnetic material.
When the present magneto-optical recording medium is irradiated with a laser beam, the recording layer stores heat, which is absorbed by the first heat sink layer, and the reproducing layer stores heat, which is absorbed by the second heat sink layer formed of a magnetic material. Furthermore, the recording layer has a magnetic domain transferred to the reproducing layer through magnetostatic-coupling. Thus in the present invention the second heat sink layer provided in contact with the reproducing layer can be formed of a magnetic material. This can prevent the reproducing layer from having a degraded magnetic characteristic.
Preferably, the magneto-optical recording medium including the heat sink layer provided for the recording layer, the heating emitting layer provided for the reproducing layer, the first reproducing layer receiving a magnetic domain transferred from the recording layer, and the second reproducing layer receiving a magnetic domain transferred from the first reproducing layer, can have the second heat sink layer formed of a magnetic material.
When the present magneto-optical recording medium is irradiated with a laser beam, the recording layer stores heat, which is absorbed by the first heat sink layer, and the first reproducing layer stores heat, which is absorbed by the second heat sink layer formed of a magnetic material. Furthermore, the recording layer has a magnetic domain transferred to the first reproducing layer through magnetostatic-coupling and in turn further transferred to the second reproducing layer through masgnetostatic-coupling. coupling. In the second reproducing layer the magnetic domain is enlarged by an external magnetic field and thus detected. Thus in the present invention the magneto-optical recording medium enlarging a magnetic domain to reproduce a signal can be provided with the second heat sink layer provided in contact with the first reproducing layer that is formed of a magnetic material. This can prevent the first reproducing layer from having a degraded magnetic characteristic.
Preferably, the magneto-optical recording medium including the heat sink layer provided in contact with the reproducing layer and opposite to the recording layer, can have the heat sink layer formed of a magnetic material.
When the present magneto-optical recording medium is irradiated with a laser beam, the reproducing layer stores heat, which is absorbed by the heat sink layer formed of a magnetic material. The reproducing layer has in an in-plane direction thereof a steep temperature profile. As such, a magnetic domain is transferred from the recording layer via the non-magnetic layer to the reproducing layer through magnetostatic-coupling with high resolution. The magnetic domain transferred to the reproducing layer is further transferred to the heat sink layer through exchanging-coupling. Thus in the present invention the magnetic domain transferred to the reproducing layer with high resolution can be detected by the heat sink layer and the reproducing layer. Consequently a reproduced signal can be increased in intensity.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.